So-called power transformers and other large electrical transformers normally comprise a core having one or several core limbs and coils wound around each core limb. Except these basic transformer components large transformers normally comprise a number of comparatively thin materials wound around each core limb. Examples of such materials are paper, wool, insulating materials, semi-conducting materials and curable or thermosetting epoxy materials. In case of curable materials, these may be applied to the core limbs in a non-cured state and cured in a thermal treatment applied after that all different windings, including the coil have been applied to the core.
For ease of manufacturing and for other reasons such additional windings may be applied by winding a comparatively narrow tape- or band-like material around the core limbs. The axial length of the core limbs is much greater than the width of the tape-like material, such that a great number axially displaced or staggered turns are needed for applying one layer of the material covering the entire length of the core limb.
One example of such windings applied to transformer core limbs is the so-called asecond. The asecond is applied by winding a tape of a non-cured epoxy material onto the core limb. The asecond winding may be applied directly onto the core limb or onto an intermediate comparatively thin layer of paper or the like. Normally a few, such as two, layers of the asecond material are wound onto the core limb. After the asecond winding has been applied, other windings including the conducting coil are wound onto the core limb and the entire core and winding package is thereafter subject to a heat treatment, whereby the epoxy material of the asecond is cured.
According to the prior art, windings of band-like materials may be applied to transformer core limbs by fixing an end of the band contained on a spool to the core limb and thereafter rotating the core limb while displacing the spool in parallel with the axis of rotation of the core limb. Such methods comprising rotating the core limb may be automated and various apparatuses for carrying out such methods are known.
It is also known to apply a winding of a band-like material around a core limb, which core limb is kept stationary during the winding process. At such methods a spool or the like containing a supply of the band-like material is manually moved around the stationary core limb.